In recent years an arrangement has become known in which a data transmission connection between a switching centre and a subscriber terminal in the public switched telephone network (PSTN) is implemented wirelessly by means of a radio connection. The arrangement is known as a wireless local loop (WLL). This arrangement avoids the installation of cables in a customer's premises. Since apparatuses, for example base stations, belonging to a network subsystem used in cellular radio networks and subscriber terminals operating over a radio connection have become less expensive, the arrangement is competitive. However, the high cost of the network infrastructure may constitute a problem since in sparsely inhabited regions, for example, the number of normal base stations required is rather great in order that broad areas can be covered.
Different smart antenna arrangements have been developed in cellular radio networks to increase the range of the base station and the traffic capacity of the system. Such arrangements are called Space Division Multiple Access (SDMA). A typical arrangement is an antenna array. For example in a base station it is possible to measure in some manner the direction where a subscriber terminal is situated with respect to the base station and to use an antenna beam oriented towards the subscriber terminal in the transmission. In the reception, the desired multipath-propagated signal components can be combined constructively by means of a smart antenna arrangement and the effect of possible interfering signals can be minimized. With the above-described arrangement it is possible, for example, to improve the carrier/interference ratio of the signal, increase cell capacity, improve connection quality, increase the battery life of the subscriber terminal and to lengthen the range.
Combining the above-described WLL and SDMA technologies creates such great costs that the arrangement is not competitive compared to a normal fixed telephone connection implemented with a cable. This is due to the fact that the receiver requires multidimensional beam searchers and trackers for each traffic channel. Multidimensional impulse response measurement is also required. If the system also employs Code Division Multiple Access (CDMA) technology, multidimensional code acquisition is required at the reception.